In a conventional digital transmission system, a transmitter sends digital signals by setting a signal parameter of an output signal such as the current or voltage of the output signal to one of a plurality of discrete values during each of a succession of intervals referred to herein as data intervals. The value of the parameter during each data interval denotes a digital value being transmitted during that data interval. For example, in a binary system, the transmitter may set the signal parameter to a first value when a digital 1 is being sent and to a second, different value when a digital 0 is being sent. The output signal from the transmitter passes to the receiver over a channel or signal path. The signal typically experiences distortion as it propagates through the signal path from the transmitter to the receiver. One type of distortion arises from temporal spreading of the signal, which results in the signal parameter during a given data interval, as received by the receiver, being affected by the signal parameter during other data intervals. This effect is referred to as inter-symbol interference (ISI). As further discussed below, ISI makes it more difficult, or impossible, for the receiver to determine the value of the signal parameter during each individual data interval. The distortion which causes ISI may arise from frequency dependent attenuation in the signal path. Typically, signal components at higher frequencies are attenuated to a greater degree than signal components at lower frequencies. It is desirable for a transmission system to compensate for this frequency dependent attenuation.